One of the primary goals of plant breeders is the continued production of improved crop plants Because of the constant change in human needs and standards, there is a concurrent, constant need for the development of new plant varieties adapted to these changing standards Nature itself does provide the raw materials upon which the necessary changes may be based, in the form of the frequent natural variation that is found to exist in many plant populations. Traditional plant breeding techniques have relied on the naturally occurring variation, combined with typical cross breeding of plant lines containing the desirable variations, to produce new varieties having the sought-after superior agronomic characteristics.
While this method has been routinely successful in producing large numbers of new plant varieties, the laborious procedures of crossing and backcrossing are timeconsuming and thus somewhat inefficient. Furthermore, not all plants exhibit a sufficient amount of natural variation or genetic combining ability to permit their routine use in plant breeding programs Therefore, new methods for producing useful variants in a rapid, reliable manner are always being sought.
The tremendous advances made in plant cell and tissue culture in recent years have provided solutions to many of the problems inherent in traditional plant breeding programs. The ability to regenerate an entire plant from a single cell or a piece of plant tissue provides the possibility of propagating large numbers of presumably identical plants from a single parent plant having a desirable variation, thus avoiding the prolonged period to establish genetic uniformity necessarily involved in more typical breeding programs. The combination of the process of regeneration with a number of different methods of artificially inducing new variations permits the production of large populations of plants containing desirable variation. For example, the technique of protoplast fusion permits the combination of the nucleus of one plant type with the nucleus or cytoplasm of another plant type to provide a unique hybrid or cybrid, from which new plants may be regenerated by cell culture.
Somaclonal variation is another technique to which new varieties are commonly obtained. This method relies on the spontaneous occurrence of a small number of variants in the process of clonal propagation. These new variations often provide a convenient source for selection of new plant types which can then be regenerated in significant numbers by cell culture techniques.
Anther culture is also a potential source in the ultimate production of plant varieties. Anther culture involves the direct development of haploid embryos from pollen or microspores. Since F.sub.1 hybrids may be heterozygous for several genes and recombination occurs during meiosis, the plants ultimately derived from pollen grains of F.sub.1 hybrids often represent different homozygous genetic recombinants, thus again providing a convenient basis for selecting raw material for new varieties. Similarly, pollen derived plants are also known to express spontaneous variations, much like those observed in plants cultured from somatic tissue. This phenomenon in pollen-derived plants is known as gametoclonal variation. Haploid breeding, in addition to providing avenues of obtaining new variants, may also reduce the time required to establish new varieties by several generations.
Although all the aforementioned in vitro techniques have contributed significantly to the recent advances in cell culture plant breeding, one of the problems inherent in their use is that the conditions required to ultimately achieve the successful production of new plants by any of these methods are almost always species- or at best genus-specific. This means that the culturing conditions which successfully yield new plants in one plant type cannot be reliably expected to operate successfully in even another closely related species. Thus, for each different species, new techniques must be developed, or else a trial-and-error procedure of modification of known techniques must be gone through in order to achieve the appropriate combination of conditions. Further, even when a successful technique is discovered for a particular species, it is frequently the case that an interspecific hybrid involving the same species will not be amenable to that technique. Thus, any known methods are assumed to be highly limited with respect to the breadth of their potential utility. Finally, although many techniques may be successful in yielding new plantlets, if the numbers of plants produced is not high, the practical utility of the method in a crop improvement program is very limited.
In connection with the present invention, however, a method of anther culture was developed with respect to the pepper, Capsicum which has been found to have a broad spectrum of applicability to production of embryos of different pepper strains. Although anther culturing of peppers has been previously described in the scientific literature (see, for example, Wang et al., Sci. Sinica, 16S:147-151, 1973), many reported techniques have not been able to produce an adequate number of plants. Subsequent work (Sibi, et al., Ann. Amerlior. Plant 20:583-606, 1979), while increasing the numbers of regenerable plants, has not produced a technique which is successful in allowing regeneration of F.sub.1 interspecific hybrids from pollen, nor have gametoclonal variants been reported from known techniques. The present method of anther cultures, however, not only reliably produces large numbers of embryos of a number of individual strains of pepper, but also, surprisingly, is effective in producing embryos from pollen of interspecific hybrids as well as reliably producing gametoclonal variants.